Method for Adjusting a Leg Prosthesis and Verifying the Adjustment, and Apparatus for the Measurement of Forces or Moments in a Leg Prosthesis

ABSTRACT

The invention relates to a method for verifying the adjustment of a prosthetic knee joint that connects a lower leg shaft, to which a prosthetic foot can be fastened, to an upper leg shaft in a manner allowing the lower leg shaft to rotate about a joint axis in order for the prosthetic knee joint to be fastened to an end of the upper leg, the upper leg shaft being movable relative to the joint axis. A knee moment and an axial force that is effective in the lower leg shaft are measured via sensors when the prosthesis is utilized. A resulting force vector with a point of attack on the upper leg shaft is calculated from said variables. The horizontal distance and the position of the resulting force vector relative to the joint axis are also calculated, and a verification is made whether and by how much the resulting force vector lies in front of or behind the joint axis on the sagittal plane. The invention also relates to an apparatus especially for carrying out the inventive method, in which connecting means are mounted on an upper prosthetic joint part so as to be movable on the sagittal plane between said upper part and an upper leg shaft while devices for detecting knee forces or moments are mounted on a terminal adapter or the upper part.

The invention relates to a method for adjusting a leg prosthesis and forverifying the adjustment, which prosthesis has a prosthetic knee joint,which pivotably interconnects an upper connection, in particular anupper leg shaft, for fixing the leg prosthesis on a wearer of theprosthesis, and a lower leg shaft, to which a prosthetic foot can befastened, the upper connection or the upper leg shaft being displaceablein relation to a joint axis. The invention likewise relates to anapparatus for determining forces and moments in a leg prosthesis, forexample a hip exarticulation prosthesis or upper leg prosthesis.

The relative position between an upper leg shaft and the actualprosthetic knee joint is of central importance for the functionality andcomfort of the prosthesis fitting. This relative position has a stronginfluence on the stability with respect to unintended bending of theprosthesis in the standing phase and on the reaction forces between theupper leg shaft and the upper leg stump. Particularly important here isthe alignment of the prosthesis in the sagittal plane, which is alsodescribed as “setup”.

In every prosthesis setup, a compromise has to be found between adequatestability in the standing phase and the least possible expenditure offorce during walking. The greater the stability in the standing phase,the greater the expenditure of force during walking. If the expenditureof force during walking is minimized, an unstable setup of theprosthetic knee joint may occur, which has to be compensated by activeuse of the hip musculature. This is disadvantageous for the user of theprosthesis.

The stability in the standing phase is achieved in principle by settingback the prosthetic knee joint or the joint axis in relation to theupper leg shaft. This ensures that the weight vector of the wearer ofthe prosthesis originating from the body extends in front of the jointaxis of the prosthetic knee joint during standing, whereby theprosthesis remains in the extended position.

During a step, the prosthesis is intended to bend into the swing phase,for which purpose the weight force vector must extend behind the jointaxis of the prosthetic knee joint. This is achieved by the patientintroducing a hip moment. As stated above, the physical force to beapplied for this purpose depends greatly on the setup of the prostheticknee joint. If the setup is too stable, the initiation in the swingphase involves great expenditure of force. This leads to prematuretiring or to pain in the upper leg stump.

At present, the positioning of the prosthetic knee joint in relation tothe upper leg shaft takes place statically and on the basis of empiricalvalues. Dynamic effects, such as for example the deformation of thesystem or of the upper leg during walking, are not taken into account.

DE 101 39 333 A1 describes a sensor device and a prosthesis with asensor device, in which the sensor device is arranged in a part of theshinbone below an artificial knee joint. The sensor device provides anouter body, formed as a closed ring, and an inner body, connecting twoopposite inner sides of the outer body and having a sensor element formeasuring the force acting in the direction of the connecting axis.Ground reaction forces for analyzing walking can be determined by thesensor device.

The object of the present invention is to provide methods and anapparatus with which a prosthesis setup improves an upper leg prosthesisand, in particular, a favorable prosthesis setup for the standing phaseof walking can be determined and adjusted.

This object is achieved according to the invention by methods with thefeatures of claims 1 and 17 and an apparatus with the features of claim19. Advantageous refinement and development of the invention arepresented in the subclaims.

The method according to the invention provides that a knee moment and anaxial force acting in the lower leg shaft are measured by means ofsensors when a prosthesis is being used. This takes place by means ofsensors which are arranged with preference in the prosthetic knee jointand in the lower leg shaft. The knee moment and the axial force are usedto calculate a resultant force vector and the distance of the forcevector from the joint axis or the knee axis normal to the axial force.The force vector may have a point of attack on the upper connection, inparticular an upper leg shaft. The normal distance in relation to thelongitudinal axis of the prosthesis, which has the same direction as theaxial force, and the position or orientation of the resultant forcevector in relation to the joint axis are calculated and it is verifiedon the basis of the normal distance whether and to what extent theresultant force vector lies in front of or behind the joint axis in thesagittal plane. If the resultant force vector lies in front of the jointaxis, the knee joint is stable, if it lies behind, the prosthetic kneejoint is referred to as an unstable joint. It is also envisaged todetermine the furthest posteriorly lying force vector in the course of astep cycle, in order to be able to observe the most unstable situationthat occurs in the course of the step cycle. Apart from distinguishingbetween a stable situation and an unstable situation, this also makes itpossible to make statements about the degree of instability. Here it isassumed overall that the force vector extends parallel to the axialforce, which is predominantly the case in prosthetics. The upperconnection may take place by means of an upper leg shaft or anosseointegrated adapter arranged on the upper leg stump. In hipexarticulation, the connection from the knee joint to the hip joint maybe regarded as the upper connection.

In a development it is provided that the ankle moment between aprosthetic foot and the lower leg shaft is detected by means of an anklemoment sensor and that, with inclusion of the ankle moment and thelength of the lower leg shaft, the resultant force vector is determined.This makes it possible to include a horizontal component of a groundreaction force in the calculation of the position of the resultant forcevector. The point of force attack of the resultant force vector on thefoot can in this case be calculated from the quotient of the anklemoment and the axial force in the lower leg shaft. This makes itpossible to determine the position of the force vector even when theaxial force is not in parallel alignment with the force vector, allowingincreased precision to be achieved in the calculation.

To make it possible for the dynamic effects during the use of an upperleg prosthesis to be taken into account in the determination andoptimization of the setup, it is envisaged to measure the knee momentand the axial force, possibly also the ankle moment, during walking anddetermine the knee moment or the resultant force vector on the basis ofa force and moment analysis over the length of the step, in the sense ofthe duration of the step, so that a statement as to whether the setup isstable or unstable can be made at any time during walking. In this wayit is possible to determine the stability of the setup of the prosthesisin the standing phase during walking, in order as a result also to beable to take account of dynamic effects in the evaluation of theprosthesis setup. The sensor data can be used to determine an axialforce, a knee moment and an ankle moment, from which in turn the vectorof the ground reaction force in the sagittal plane is determined. Forbetter visualization of the results in a system of inertial coordinatesand an exact assignment of the respective values to the phases of astep, it is provided that the resultant force vector is determined bydetermining the current knee angle, for example by means of a knee anglesensor or an upper leg angle sensor, which determine the absolute anglesin relation to a vertical line. With a known upper leg angle, aconversion can be made from a system of coordinates that is fixed forthe prosthesis into a system of inertial coordinates. However, it issufficient for the setup analysis to consider a system of coordinatesthat is fixed for the prosthesis, which can be carried out withouttaking account of the current knee angle, it being possible foridentification of the swing phase to be carried out by way of the axialforce determination. If the axial force value is zero or if tensileforces are measured instead of compressive forces, it is to be assumedthat a swing phase is occurring. The knee angle may be used inparticular for estimating the hip moment.

Furthermore, it is provided that the angle between the lower leg shaftand the prosthetic foot is determined in order to detect the plantarflexion of the foot in relation to the lower leg shaft. This isrequired, since the pointed foot position has a strong influence on thestability or instability of the prosthetic knee joint. By increasing thepointed foot angle, a hyperextending moment, consequently with astabilizing effect, is produced within the prosthetic knee joint, sothat a poor set-back adjustment can be partially compensated by changingthe pointed foot angle. In particular, the pointed foot position has agreat influence on the variation of the knee moment and the anklemoment, the extension element that is necessary to initiate the swingphase becoming smaller as the pointed foot angle becomes smaller, andsetup of the extension moment being commenced later. The greater thepointed foot angle, the shorter the time during which the heel of theprosthetic foot is under load.

Should it be found that the resultant force vector in the standing phaseduring walking is situated behind the joint axis of the prosthetic kneejoint, that is to say that there is an unstable setup in the standingphase, it is provided that the joint axis is adjusted or displaced untilthe resultant force vector extends in front of the joint axis or untilthe joint axis is arranged behind the resultant force vector. Apart fromthe knee joint axis, a joint axis of the prosthetic foot may also bedisplaced in order to achieve a stable prosthesis setup. Likewise, inaddition or as an alternative, the extension stop of the knee joint andthe extension stop of the foot joint, that is to say the dorsal stop,may be changed, in particular changed synchronously. If the dorsal stopof the foot joint and the extension stop of the knee joint are adjustedoppositely in relation to each other, the flexion of the upperconnection or upper leg shaft is changed, which does not lead tocorresponding results in comparison with a displacement of the axes ofrotation. The flexion of the upper leg shaft would not be ideal for thestatic setup, but can be used to distinguish between standing andwalking. Therefore, an iterative evaluation process is carried out todetermine the setup, a process in which the position of the resultantforce vector in relation to the joint axis is determined and theprosthesis setup is changed until a sufficiently stable setup in thestanding phase in the course of the walking cycle is achieved. If thepatient would like a dynamic setup, the prosthesis is adjusted in such away that the force vector extends directly in front of the joint axis.However, the method and the setup adjusting system show where the forcevector extends, so that a qualified and quantitatively recorded,possibly documented, adjustment of the prosthetic knee joint can beperformed.

In particular in the case of electronically controlled knee or footjoints, the displacement of the joint axes or the changing of theextension or dorsal stops can be effectively used by distinguishingbetween walking and standing. During walking, a set-back displacementthat is as small as possible is desired in order to minimize theexpenditure of force; during standing, a stable set-back displacement isdesired in order to ensure a stable prosthesis setup and stablestanding. The currently active moments are determined by means of anklemoment and knee moment sensors. Adjustable stops, for example arrestablehydraulic cylinders with corresponding actuators, adjust the optimumposition of the joint axes or of the stops in dependence on the measuredmoments and the determined vector position, the position to be adoptedbeing prescribed on the basis of empirical data or personal preferenceof the prosthesis user.

Since changing the setup, in particular displacing the joint axis or thejoint axes or the stops has the effect of changing the alignment of theprosthetic foot, it is envisaged to mark the relative position of theprosthetic foot with respect to the lower leg shaft before thedisplacement of the joint axis and to restore the relative position ofthe prosthetic foot with respect to the lower leg shaft after thedisplacement of the joint axis. This ensures that the geometricrelationships that are changed by the adjustment of the joint axis donot have any effect on the alignment of the foot.

A simple method for marking and restoring the original adjustment of theprosthetic foot provides that the relative position of the prostheticfoot with respect to the lower leg shaft is determined by a laserpointer being fixedly arranged on the upper leg shaft. A laser beam isdirected onto the prosthetic foot and the point of impingement ismarked. After the displacement of the joint axis, if the laser pointeris unchanged the prosthetic foot is adjusted in such a way that themarking is made to coincide again with the laser beam. Instead of alaser pointer, other marking means, in particular optical marking means,may also be used.

After the displacement of the joint axis and the alignment of theprosthetic foot, the plantar flexion adjustment of the prosthetic footmay also be corrected. For this purpose, it is provided that, before thedisplacement of the joint axis, a reference line is drawn from the upperleg shaft to the prosthetic foot and, after the displacement of thejoint axis, the prosthetic foot is aligned in such a way that thereference line is made to coincide again, so that it is ensured that theprosthetic foot is on a horizontal plane, as it originally was. If thereference line coincides with the axis of an adjusting core between theknee joint prosthesis and the prosthetic foot, that is to say in theregion of the ankle, an error in the shaft preflexion can be largelyavoided. The reference line may be placed through a distal adjustingaxis of the prosthetic knee joint.

A development of the method provides that the current hip moment isdetermined by determining the resultant force vector and the givengeometry of the prosthesis. In an ideal case, the prosthetic leg shouldhave only small hip moments while standing or during the standing phase.If this is not the case, the moments in the two hip joints are notequal, so that horizontal forces occur.

The method for adjusting a leg prosthesis which has a prosthetic kneejoint, which pivotably interconnects an upper connection for fixing theleg prosthesis on a wearer of the prosthesis, and a lower leg shaft, towhich a prosthetic foot is fastened, the upper connection beingdisplaceable in relation to a joint axis of the prosthetic knee jointand/or the position of the prosthetic foot in relation to the lower legshaft, provides that a knee moment and an axial force are measured bymeans of sensors when a prosthesis is being used, the knee moment andthe axial force being used to calculate a resultant force vector, andthat the normal distance in relation to the joint axis and the positionof the resultant force vector in relation to the joint axis arecalculated and it is verified whether and to what extent the resultantforce vector lies in front of or behind the joint axis in the sagittalplane, and an adjustment of the upper connection in relation to the axisof the prosthetic knee joint and/or extension stops for the prostheticknee joint and/or a prosthetic foot joint is performed in dependence onthe determined position of the resultant force vector.

The knee joint axis, the foot joint axis and/or the extension stops maybe adjusted in such a way that the resultant force vector lies in frontof the knee joint axis during the standing phase.

The apparatus according to the invention for the measurement of forcesor moments in a leg prosthesis, in particular in an upper leg prosthesisor hip exarticulation prosthesis, with a prosthetic knee joint, forverifying adjustment or for adjusting a prosthesis setup, provides thatthere is an upper part for the connection to an upper connection, inparticular an upper leg shaft, and a lower part jointly connected to theupper part, connecting means being provided for fastening the upper partto the upper connection, the connecting means preferably having anadapter mounted displaceably in the sagittal plane on the upper part anddevices for detecting knee forces or knee moments being provided on theconnecting means or on the upper part. The apparatus makes it possibleto detect the effective forces and moments within a prosthetic kneejoint and, in addition, preferably by adjusting the connecting means,determine or change the position of the joint axis in relation to theupper leg shaft in such a way that an optimum prosthesis setup can beachieved. The adapter may in this case be fixed on the upper part bymeans of a clamping device. As an alternative to this, adjusting screwsthat are accessible from the outside may be provided, for example in theform of a spindle, by means of which the joint axis can be comfortablydisplaced in relation to the upper part or the upper connection, inparticular an upper leg shaft, in order that the prosthesis setupchanges, and the findings thereby obtained concerning the prosthesissetup can be directly verified in practice.

A refinement of the invention provides that arranged between the upperpart and the adapter is a bridge element and/or a carrier, on which theadapter is displaceably mounted. The bridge or the carrier is in thiscase fastened to the upper part in a preferably moment-resistant mannerand forms an intermediate piece which is situated between the adapterarranged directly on the upper leg shaft and the upper part and isappropriately designed for determining the forces and moments that areeffective in the knee joint. A measuring beam which, when subjected tomoments or forces, deforms to such a degree that the effective kneeforces and knee moments can be clearly determined with a high measuringsignal, for example by means of strain gages, may be formed on thebridge. This provides an inexpensive refinement of a bidirectionalmeasuring unit. However, the measuring beam must be dimensioned in sucha way that the bridge does not fail and the structure remains intacteven when maximum load values are reached. The adapter or the adapterwith the bridge and the carrier are preferably designed in such a waythat the fitting height corresponds to the fitting height of theconnecting means that are used after the adjustment of the prosthesissetup. In the case of this variant, it is provided that, once theoptimum prosthesis setup has been determined, the device is removed andreplaced by the normal connecting means.

An exemplary embodiment of the invention is explained in more detailbelow on the basis of the figures, in which:

FIG. 1 shows a schematic representation of a leg prosthesis with sensorsarranged in it;

FIG. 2 shows a representation of the effective forces in an arrangementaccording to FIG. 1;

FIG. 3 shows a perspective representation of the moments and relativeforces as well as angles;

FIG. 4 shows a schematic representation of FIG. 3;

FIG. 5 shows the relationship between the variation of the knee momentand a set-back displacement;

FIG. 5 a shows a schematic representation of an adjustment of extensionstops;

FIG. 6 shows a schematic representation of the restoration of the footposition;

FIG. 7 shows a schematic representation of the restoration of theplantar flexion;

FIG. 8 shows an exemplary embodiment of the apparatus according to theinvention in the assembled state;

FIG. 9 shows a variant of FIG. 8 in a turned position;

FIG. 10 shows a plan view of the apparatus; and

FIG. 11 shows a sectional representation along A-A of FIG. 10.

Represented in FIG. 1 is a leg prosthesis 1 with an upper leg shaft 2,which can be fastened to an upper leg stump that is not represented.Fastened to the upper leg shaft 2 is a knee joint 3, which is mountedpivotably about a knee axis 31. Fastened to the prosthetic knee joint 3is a lower leg shaft 4, which connects the knee joint 3 to a prostheticfoot 6 by means of a coupling point 5. Provided in the knee joint 3 is asensor 10 for measuring the knee moment M_(K), the measuring axis 31 ofthe sensor 10 corresponding to the joint axis of the knee 3. The kneeangle φcan be determined either by means of the sensor 10 or anothersensor, for example in the lower leg shaft 4. An osseointegrated upperconnection, which connects the knee joint 3 to the upper leg stump, maybe provided as an alternative to an upper leg shaft 2. In the case ofhip exarticulations, there is no upper leg stump, so that the connectionfrom the knee joint 3 to the hip joint is regarded as the upperconnection.

To determine an ankle moment M_(T), a sensor 11 is arranged in theconnecting region between the lower leg shaft 4 and the prosthetic foot6 for the measurement of an effective axial force F_(AX) within thelower leg shaft 4 and the ankle moment M_(T); the measuring axis 51 ofthe sensor 11 lies parallel to the knee axis 31.

In FIG. 2, the heights and lengths as well as the orientations of theforces and moments are shown; the height of the ankle moment sensor 11or the sensor axis 51 is denoted by H_(S).

The distance of the knee axis 31 from the measuring axis 51 of the anklemoment sensor 11 is denoted by L_(T). Just like the knee moment M_(K),the ankle moment M_(T) is shown positively in the counterclockwisedirection, acting upward in just the same way as the axial force F_(AX)in the lower leg shaft 4, that is to say it is assumed to be positive inthe direction of the knee joint 3.

In FIG. 3, further effective forces are shown in a perspectiverepresentation, the one contact force F_(K) being assumed to be theground reaction force F_(GRF), which is always regarded as beingpositively effective in the y direction, according to the system ofcoordinates in FIG. 4. If the upper leg shaft 2 is pivotedcounterclockwise by an angle φ, a resultant force F_(R) acts counter tothe contact force F_(K), the distance λ, as the normal distance of theforce vector F_(R) from the knee axis 31, being an indicator of whetherthe setup at a given time of the prosthetic knee joint 3 is stable orunstable. The information indicated by the model applies to any systemof coordinates that is considered, that is to say also to a system ofcoordinates that is fixed with respect to the lower leg. If an appraisalof the conditions at the hip is not required or is not of interest, noknee angle information is required.

In the situation represented in FIG. 4 of the heel touching down with anangle ξ between the longitudinal axis of the prosthesis and thevertical, λ is negative, so that the resultant force vector F_(R) in thesagittal plane lies behind the joint axis 31. The prosthetic knee joint3 would consequently be unstable. To be able to provide a stableprosthesis setup, the joint axis 31 would have to be displaced in thenegative x direction in the sagittal plane. A set-back displacement ofthe joint axis 31 consequently has a significant influence on thevariations of the knee moment, ankle moment and axial force.

In the case of a stable prosthesis setup, the knee moment at any givenpoint in time in the standing phase should depend linearly on theset-back displacement on account of the mechanics present, that is tosay on account of the lever lengths present. If the prosthesis setup isvery unstable, the wearer of the prosthesis must actively prevent theprosthesis from bending away from under him by applying a hip extensionmoment. In theory, this acts as a reduction of the maximum knee momentin the standing phase. In principle, a prosthesis should be set up insuch a way that a standing phase flexion is possible, since impact oncontact when the prosthesis is placed on the ground is reduced as aresult. For this reason, the prosthesis setup should not be set back toofar, in order to permit a certain bending moment, but without forcingthe wearer of the prosthesis to actively prevent further bending of theprosthesis. However, a prosthesis setup should cater for the individualwishes of the prosthesis user. The permissible flexion moment in thestanding phase is subject to highly individual differences, which arealso subject to dynamic influences, so that the optimum alignment of thejoint axis generally cannot be obtained by carrying out alignment in thestatic state in the way so far necessarily determined by laboriousseries of tests. This adjusting procedure can be significantly curtailedby the method according to the invention and the apparatus according tothe invention.

Shown by way of example in FIG. 5 is the relationship between thevariation of the knee moment and a set-back displacement over a stepcycle. The time is normalized here as a percentual step length, 100%corresponding to a full step cycle. Represented in millimeters on thesecond horizontal axis is the set-back displacement of the joint axiswith respect to an assembly reference line, that is to say theconnecting line from the middle of the lower leg shaft to the middle ofthe prosthetic foot. A knee moment value of zero marks the transitionfrom a stable prosthesis setup to an unstable prosthesis setup. With apositive knee moment, an unstable prosthesis setup is achieved. With atransition from a stable setup to an unstable setup, a stability limitis reached, constituting a sensible guide value for the adjustment ofthe prosthesis setup from the standing phase flexion. If the position ofthis stability limit is known, it is easy to cater for the individualneeds of a prosthesis user by displacing the prosthesis back in adesired stable setup; with a desired dynamic setup, a set-forwarddisplacement can take place.

A further parameter with an influence on the stability of the prosthesissetup is the pointed foot adjustment. By increasing the pointed footangle with more plantar flexion, a hyperextending moment, whichtherefore has a stabilizing effect, is produced in the knee. Inprinciple, a suboptimal set-back adjustment can be compensated bychanging the pointed foot adjustment, the prosthetic knee joint beingextended very early with a great pointed foot angle. The requiredextension moment for initiating the swing phase is then great and mustbe applied for a relatively long time. The smaller the pointed footangle, the smaller the extension moment necessary for initiating theswing phase, and the later the setting up of an extension moment iscommenced. The pointed foot angle also has an influence on the variationof the knee moment when the prosthesis is under load, the aim of thepointed foot angle adjustment being to provide a variation of the kneemoment that is as uniform as possible.

To be able to verify the adjustment of a prosthetic knee joint duringuse, it is necessary to determine the normal distance λ of the resultantforce vector F_(R) from the knee axis 31 at each point in time orsampling point during the standing phase. To be able to obtain thenormal distance λ, it is necessary to determine the orientation and thepoint of attack of the resultant force vector F_(R) or the groundreaction force F_(K). Since only a displacement within the sagittalplane is to be considered for assessing whether the prosthesis setup inthe standing phase is in a stable or unstable state, a planar problem isconcerned. It is possible to determine the resultant force vector F_(R)or the corresponding contact force F_(K) in its position and orientationfrom the ankle moment sensor 11 as well as the sensor for determiningthe axial force F_(AX) and the sensor 10 for determining the knee momentM_(K) as well as the previously determined lengths H_(S) and L_(T).Everything which happens above the knee joint 3 can thereby be reducedto the resultant force F_(R), which means in particular that no activelyapplied hip moments M_(H) are taken into account and that the influenceof a horizontal component of the ground reaction force F_(GRF) on theankle moment M_(T) is negligible. The assumption that the hip momentM_(H) is negligible can be correctly made if the prosthesis setup is notextremely unstable. To be able to take account of hip moments M_(H), atleast one further sensor would have to be provided, which would be toocomplicated.

To be able to appraise the hip moment M_(H), a calculation can be madewith the determined contact force F_(K) by way of the equilibrium ofmoments at the hip joint with M_(H)=L₂*F_(K) and the relationshipL₂=L_(F)*sin(φ−α)+λ, and with L_(F) as the measured length of the upperleg and L₂ as the distance of the resultant force vector from the pointof attack of the hip moment M_(H) with the knee angle φ. To be able tocalculate the effective lever length L₁ at the height of the anklemoment sensor 5, the quotient of the measured ankle moment M_(T) and theaxial force F_(AX) in the lower leg shaft is formed. The lever length L₁indicates the distance of the force entry point of the ankle joint atthe height of the ankle moment sensor 11. The equilibrium of moments atthe ankle joint is M_(T)=−L₁×F_(K).

For the explicit calculation of the vertical component of the contactforce F_(K), the equation M_(T)=F_(AX)·L₁−F_(KX)·H_(S) iscorrespondingly resolved. The knee moment M_(K) corresponds to thenegative product from the normal distance λ and the contact force F_(K).The equilibrium of forces at the lower leg shaft 4 with F_(K)cos(α)+F_(AX)=0 and the geometric relationship sin(α)=(λ−L₁)/L_(T)provides a nonlinear system of equations from which the values soughtcan be calculated.

In this case, the angle α is the angle between the force vector and thelongitudinal axis of the prosthesis. F_(KX) and F_(KY) are contact forcecomponents in the X and Y directions. The calculation of the requiredvariables F_(KX), F_(KY), L₁ and λ is performed in a computer into whichthe geometric variables and dimensions as well as the measured moments,angles and forces are entered. The current measured values can be sentinto the computer by way of an interface, the dimensions can be enteredmanually. The fact that the normal distance λ of the ground reactionvector F_(GRF) or of the contact force vector F_(K) from the knee axis31 can be calculated at each point in time of the standing phase meansthat it is also possible at each point in time of the standing phase todetermine whether the prosthesis setup is stable or unstable. Whetherthe setup is stable or unstable can be established by a comparison ofthe determined distance with a defined distance for a stable or unstableor dynamic setup.

To further optimize the prosthesis setup, the pointed foot adjustmentmust be chosen such that the force vector while standing extends throughthe middle of the foot. This can be realized by means of a rockerarrangement, on which a person with the prosthesis stands in such a waythat the middle of the plate is located at the desired position of loadintroduction of the prosthetic foot. By means of a marking on the plate,the middle of the foot can be brought over the turning point, the heeland toes having to be spaced at equal distances from the marking. Whenstanding in a relaxed position, the plantar flexion can be changed untilthe plate is in equilibrium and rocks on a rod provided underneath themarking. As soon as equilibrium is reached, the point of origin of theforce is in the middle of the foot.

After the plantar flexion adjustment has been carried out and themeasurement of the moments and forces within the prosthesis and thedetermination of the character of the prosthesis setup, the joint axisis displaced to the front or to the rear in the sagittal plane by anamount λ′. The necessary displacement λ′ to achieve a target moment ofM′ in the knee joint 3 in the standing phase flexion can be calculated.Alternatively, the displacement may take place by changing the extensionstops in the opposite direction by arctan (λ′/L_(T)).

Shown in FIG. 5 a is a schematic representation of a leg prosthesis inwhich the upper leg shaft 2 is connected to the lower leg 4 by means ofthe prosthetic knee joint with the joint axis 31. The lower leg 4 bearsat its distal end a prosthetic foot 6, which is pivotable by means of ajoint axis 61 and fastened in a possibly adjustable manner to the lowerleg shaft 4. Between the lower leg shaft 4 and the upper leg shaft 2there is an adjustable extension stop 24, which is indicated by anarrow. This extension stop 24 can be changed, for example in such a waythat the prosthetic foot 6 is displaced further forward. Then theprosthetic foot 6 is in the position 6′ shown by dashed lines, while thelower leg shaft 4′ is pivoted forward in the walking direction. Theextension stop 24′ then taken up by the knee joint 3 has been adapted torealize a stable or dynamic setup in dependence on the determinedposition of the resultant force vector. At the same time, the dorsalstop 46 of the prosthetic foot 6 can either be adjusted synchronously,in which case the dorsal stop 46′ present brings about an adaptation ofthe position of the foot. The adjustment of the extension stops 24, 46may take place under electronic control by means of actuators, forexample lockable hydraulic cylinders. Consequently, an adaptation todifferent prosthesis users or different operating conditions can beperformed. It is likewise possible that, when there is a displacement ofthe lower leg 4 in relation to the joint axis 31, the position of theprosthetic foot is automatically corrected, so that a prosthesis setupaccording to the requirements envisaged by the prosthesis user can berealized in dependence on the actually existing prosthesis setup, theoperating conditions and the position of the prosthesis on theprosthesis user.

To align the position of the foot as before after an adaptation of theset-back displacement by adjustment of the knee axis 3, before theadjustment a light spot is applied to the upper side of the prostheticfoot 6 and marked by means of a laser pointer 7 fastened to the upperleg shaft 2, as shown in FIG. 6. Subsequently, the joint axis 3 isdisplaced by the calculated amount λ′. After the displacement, theprosthesis is turned until the projected point coincides again with themarking.

Likewise, before the set-back displacement, the pointed foot adjustmentor plantar flexion of the prosthetic foot 6 should be checked. Thisadvantageously takes place after the alignment of the prosthetic foot asdescribed above by means of a laser pointer. When restoring the originalplantar flexion, screws on an ankle pyramid 9 are loosened, the wearerof the prosthesis standing comfortably so that the system can settle andthe sole of the shoe rests flat on the ground. Then the screws aretightened again. Alternatively, for the adjustment of the plantarflexion, the rocker described above may be used or a continuousreference line 9 drawn on the shaft 4 and the prosthetic foot 6 beforethe set-back displacement.

After the set-back displacement, the possibly offset parts of the lineare brought into line with one another, so that the original pointedfoot adjustment is restored. After the first set-back displacement, thealignment of the prosthetic foot 6 and the plantar flexion correction,the prosthesis setup is evaluated once again over a number of stepcycles on a level surface and possibly corrected.

Finally, the maximum loads occurring are checked. If a satisfactoryadjustment has been found, the moment sensor in the prosthetic kneejoint 3 can be replaced by a suitably adjusted displacing adapter.

The moment sensor is in this case advantageously set up according toFIG. 8, in which a pyramid socket 30 for introduction into the upper legshaft is arranged. The pyramid socket 30 is fixed in a desired positionon a carrier 34 by means of a clamping device 32, which is representedin detail in FIG. 10. As indicated by the double-headed arrows, thepyramid socket 30 is displaceable along the axis of the arrows, thepyramid socket 30 being held unchangeably in the longitudinal directionby means of a wedge guide. Arranged on the pyramid socket 30 is a holder17 for a laser pointer 7. The laser pointer 7 and the holder 17 areventrally arranged, the holder 17 being mounted pivotably about an axisof rotation in the transversal plane. Likewise, turning of the laserpointer 7 about an axis in the sagittal plane is provided by itsmounting. The clamping device 32 can be released and can be locked bymeans of clamping screws 39′, which are accessible through bores 33lying in the sagittal plane, so that the pyramid socket 30 can bedisplaceably fixed on the carrier 34. The pyramid socket 30, the carrier34 and the bridge element 35 form the connecting means for fastening theupper part (not represented) of the prosthetic knee joint to the upperleg shaft.

Fixed on this carrier 34 is a bridge element 35, which in turn isfastened to the upper part (not represented) of the knee joint. Providedon this bridge element 35 are strain gages 37, as shown in FIG. 9, todetermine the forces and moments acting on the prosthetic knee joint 3.In FIG. 8, the strain gages 37 are protected by a protective cover 36.The bridge element 35 forms the measuring beam and, for reasons ofspace, is aligned with the open limbs distally disposed. To achieve themost homogeneous possible deformation of the bridge element 35 or of themeasuring beam, the latter is jointly connected to the upper part of theprosthesis. For this purpose, a turning joint 38 and a sliding joint 38′are formed at the connection to the upper part of the prosthesis, theturning joint 38 permitting turning on the basis of elasticdeformations, while the sliding joint 38′ allows linear compensation,and consequently prevents longitudinal stresses. The mounting on theupper part is arranged below the axis of rotation 31.

FIG. 9 shows in a view from the rear the moment sensor with the straingages 37, which are arranged between the joint axis 31 and the slidingjoint 38′ or turning joint 38.

Shown in plan view with a partial detail in FIG. 10 is the clampingdevice 32, which displaces a clamping wedge 39 by means of clampingscrews 39′. If the clamping screw 39′ assigned to the laser pointer 7 isscrewed in, a force is exerted in the direction of the frontal plane byway of the clamping wedge 39, whereby the pyramid socket 30, which isformed here as a displacing adapter, is fixed on the carrier 34. Areverse turning movement of the clamping screw 39′ has the effect thatthe clamping wedge 39 is made to move in the other direction, and theclamping is accordingly released. The clamping screw 39′ is in this caseformed in such a way that access is possible from both sides. It ispossible by appropriate mounting of the clamping screw 39′ that both theopening and the closing of the fixing or clamping are possible from bothsides.

Connectors 40 or interfaces, which permit the reading out of sensor dataand transmission to an evaluation device, for example a computer, areformed on the upper side of the holder 34. A section A-A, which is takenin the frontal plane, is represented in FIG. 11. In this section, thewedge guide of the pyramid socket 30 in the carrier 34 can be seen, ascan the clamping device 32 with the clamping screw 39′ and theinterfaces 40 with respect to a PC.

Once the evaluation of the prosthesis setup has taken place, the entireapparatus for detecting the knee moments, with the pyramid adapter 30,the carrier 34, the bridge element 35 and the strain gages 37, can beexchanged for conventional adapters for fastening the prosthetic kneejoint 3 to the upper leg shaft 2. For this purpose, the dimensions ofthe apparatus are made to be similar to those of the conventionaladapters. It is also possible always to use the apparatus represented,the measured values constantly being evaluated by a computer andpossibly evaluated for controlling damper devices. In the case of anenvisaged exchange, the data are transmitted by way of the interfaces 40to a computer, which calculates over which path a displacement of thepyramid adapter 3 must take place in relation to the joint axis 31 inorder that a stable, neutral or dynamic setup is achieved. The degree ofadjustment or the present fitting situation can be output on a display.

As an alternative to the embodiment represented, other knee momentsensors may also be provided and used.

1.-26. (canceled)
 27. A method for verifying the adjustment of a legprosthesis, wherein the leg prosthesis includes a prosthetic knee jointpivotally connected to an upper connection and a lower leg shaft,wherein the upper connection fixes the leg prosthesis on a user of theleg prosthesis and the lower leg shaft fastens to a prosthetic foot, andwherein the upper connection is displaceable in relation to a joint axisof the prosthetic knee joint, the method comprising: measuring a kneemoment and an axial force by means of sensors when the leg prosthesis isbeing used; calculating a resultant force vector using the knee momentand the axial force; calculating a normal distance relative to the jointaxis and the position of the resultant force vector in relation to thejoint axis; and verifying a position of the resultant force vectorrelative to the joint axis in the sagittal plane.
 28. The method ofclaim 27, further comprising calculating the resultant force vector witha point of attack on the upper connection.
 29. The method of claim 28,wherein calculating the resultant force vector with a point of attackcomprises calculating the resultant force vector from a quotient of anankle moment and an axial force in the lower leg shaft.
 30. The methodof claim 27, further comprising determining the normal distance of theresultant force vector from the joint axis.
 31. The method of claim 27,further comprising detecting an ankle moment by means of an ankle momentsensor, wherein the resultant force vector is determined with inclusionof the ankle moment, the knee moment, the axial force and a length ofthe lower leg shaft.
 32. The method of claim 31, wherein determining theaxial force, knee moment and ankle moment comprises using the data fromthe sensors, from which a vector of the ground reaction force in thesagittal plane is determined.
 33. The method of claim 27, whereinmeasuring the knee moment and the axial force occur during walking. 34.The method of claim 27, further comprising determining the current kneeangle and/or the upper leg angle in relation to the vertical line todetermine a resultant force vector.
 35. The method of claim 27, furthercomprising determining an angle between the lower leg shaft and theprosthetic foot, wherein the knee moment and/or an ankle moment arecalculated based on detection of the angle.
 36. The method of claim 27,wherein when the resultant force vector is positioned behind the jointaxis during a standing phase, the joint axis is displaced to behind theresultant force vector.
 37. The method of claim 36, further comprising:marking a relative position of the prosthetic foot with respect to thelower leg shaft before displacing the joint axis; and restoring therelative position of the prosthetic foot with respect to the lower legshaft after displacement of the joint axis.
 38. The method of claim 37,further comprising fixing the relative position of the prosthetic footby a laser beam being directed onto the prosthetic foot by means of alaser pointer fixedly arranged on the upper leg shaft, wherein a pointof impingement marked and the marking on the prosthetic foot are alignedwith the laser beam after displacement of the joint axis.
 39. The methodof claim 36, further comprising correcting a plantar flexion adjustmentof the prosthetic foot after the displacement of the joint axis.
 40. Themethod of claim 39, further comprising drawing a reference line from thelower leg shaft on the prosthetic foot and the lower leg shaft beforedisplacing the joint axis to correct the position of the plantar flexionof the prosthetic foot before displacing the joint axis.
 41. The methodof claim 40, further comprising aligning the prosthetic foot such thatthe reference line coincides with the joint axis after displacing thejoint axis.
 42. The method of claim 40, wherein drawing the referenceline comprises placing the reference line through an adjusting axis ofthe prosthetic knee joint.
 43. The method of claim 27, furthercomprising determining a current hip moment by determining the resultantforce vector and a given geometry of the prosthesis.
 44. A method foradjusting a leg prosthesis having a prosthetic knee joint pivotallyconnecting an upper connection for fixing the leg prosthesis on aprosthesis user and a lower leg shaft to which a prosthetic foot isfastened, wherein the upper connection is displaceable in relation to ajoint axis of the prosthetic knee joint and/or the position of theprosthetic foot in relation to the lower leg shaft, the methodcomprising: measuring a knee moment and an axial force by means ofsensors when the prosthesis is being used; calculating a resultant forcevector using the knee moment and the axial force; calculating a normaldistance in relation to the joint axis and the position of the resultantforce vector in relation to the joint axis; verifying a position of theresultant force vector relative to the joint axis in a sagittal plane;and adjusting the upper connection in relation to an axis of theprosthetic knee joint and/or extension stops for the prosthetic kneejoint and/or a prosthetic foot joint based on the position of theresultant force vector.
 45. The method of claim 44, wherein adjustingthe upper connection comprises adjusting a knee joint axis, a foot jointaxis, and/or an extension such that the resultant force vector lies infront of the knee joint axis when standing.
 46. An apparatus formeasuring forces or moments in a leg prosthesis having a prostheticjoint comprising: an upper part connectable to an upper connection forfastening to a user of the prosthesis; a lower part jointly connected tothe upper part; connecting means for fastening the upper part to theupper connection; and means for detecting knee forces and momentsprovided on one of the connecting means and the upper part.
 47. Theapparatus of claim 46, wherein the connecting means has an adaptermounted displaceably in a sagittal plane on the upper part.
 48. Theapparatus of claim 47, wherein the adapter is fixed on a holder by aclamping device.
 49. The apparatus of claim 47, further comprising acarrier and/or bridge element arranged between the upper part and theadapter, wherein the adapter is displaceably mounted on the carrier andthe carrier is fixed to the upper part.
 50. The apparatus of claim 49,further comprising a strain gage for determining effective knee forcesand moments provided on the bridge element.
 51. The apparatus of claim47, wherein the adapter has a fitting height that corresponds to afitting height of the connecting means that is used after adjustment ofthe prosthesis setup.
 52. The apparatus of claim 46, further comprisinga carrier for a marking device fastenable to the connecting means. 53.The apparatus of claim 46, wherein the upper connection is formed as anupper leg shaft.